[GRASS-user] new user question about mapsets, locations, and coordinate systems

[Hamish]

mtnbiketrail wrote:
> I'm using 6.3 on Ubuntu with QGIS.
> If I create a new location, under PERMANENT, does that
> coordinate system that I specify for PERMANENT the default
> coord sys for a new mapset I create under that location?

yes.

see:
 http://grass.osgeo.org/intro/firsttime.php#location
 http://grass.ibiblio.org/grass64/manuals/html64_user/helptext.html
 http://grass.osgeo.org/wiki/GRASS_Help#First_Day_Documentation


> I have different raster and vector maps I want to use and they
> are all different coord systems. Can I have a different
> coord system for each mapset?

no, all mapsets within a location use the same SRS. The spatial reference
system details are stored in the $MAPSET/PERMANENT/PROJ_INFO file.

 
> For the DATABASE parameter, is GRASS smart enough to add on
> the LOCATION directory.

? not sure I understand the question. a single "database" (where you keep
all your grass data) can contain many locations.

> IS the DATABASE always the same, even if I create different LOCATIONS?

yes, typically /home/you/grassdata/ or so.

 
> So should I create the PERMANENT coord system with what I
> want to use( which is wgs84 UTM).

yes. then use v.proj and r.proj to pull in maps from other locations/proj's.

> So I can use QGIS and its "on the fly" option.

be very careful with that if your various map projections do not share
the same datum, it is likely that the data may be 100m+ off. I've not
tested the latest qgis version but that used to be a problem. The same
was true for the "on the fly" mode of the leading commercial GIS software
last time I checked a few months ago, it's rather hard to get right
apparently.

GRASS generally does not do "on the fly" (as I've never seen that done
bug-free maybe that's a good thing), but within your projection you can
overlay lat/lon grids and get WGS84 lat/lon coordinates from a number of
modules.


> I tried to do this with the text based interface, but kept
> getting weird stuff, like ESC+ENTER didn't always work.

could you expand on that? the esc+enter code is literally decades old
and thus extremely well tested. but that's not to say there isn't 
some other weirdness creeping in.



Hamish